The present invention relates to highly lint-free wipers, particularly to lint-free wipers which are often used in clean rooms or production processes of precision instrumental parts or electronics parts including, typically, LSIs, or production processes of pharmaceuticals or medical instruments, which environment must be controlled to be free from fine dust, fibrous waste or the like.
Articles used in a clean room or a room in which the environment is controlled are required to have special performances necessary for maintaining the environment. In particular, the articles are required to hardly generate fine dust, fine debris of material or others (hereinafter referred to as lint). As is well known, contaminants or lint brought in the clean room are often derived from the operators themselves and articles used thereby. Accordingly, a special attention has been paid to articles such as working clothes or wipers and the improvement thereof has continued.
One of the potential sources of contamination with fineparticles in a clean room is a wiper for a daily wiping operation carried out therein. For example, wipers have been used for wiping up stains in the operation steps of producing or assembling semiconductors or integrated circuits. Also, wipers have been widely used for cleaning surfaces of various apparatuses or fixtures and cleaning inner walls or interiors of rooms. Since the wiper of this kind must be excellent in liquid absorption property and flexibility, it has become a structural obstacle for preventing fine particles or fibrous waste from being released and dispersed in the surrounding environment.
Materials for wipers used in clean rooms are discriminatingly selected in accordance with the degrees of cleanness required for the particular room from a group of a knitted fabric, a woven fabric, a non-woven fabric, sponge, paper or others. In a room where a high degree of cleanness is required, a knitted fabric or a woven fabric composed of synthetic fiber is particularly often used. In a room, where a relatively low degree of cleanness is required, a non-woven fabric mainly composed of cellulosic fiber is often used.
Generally speaking, a wiper used in a clean room is usually formed of a flat cut piece of a knitted fabric, a woven fabric or a non-woven fabric having a rectangular shape or others. In the wiper of this kind, edges of the wiper coincide with cut edges of the fabric. Since the wiper has such a structure, the edge portion and the end surface thereof are often fused to be of a film-like structure or are heat-sealed.
On the other hand, as fibrous material for constituting a wiper-forming fabric, fibers made of thermoplastic polymer, especially multi-filamentary yarns have been usually used. This is because, if a knitted fabric or others composed of such yarns is cut by a heat cutter or an ultrasonic wave cutter, the single filaments thus cut easily fuse and adhere, and hardly separate from the fabric whereby the generation of dust from the cut face is suppressed. Thus, there is a limitation in that non-thermoplastic or non-melting fibers such as cellulosic fibers are difficult to use for this purpose.
While polyester fibers are often used as the thermoplastic synthetic fibers for the wiper, they are poor in water-absorption property and, if a hydrophilic treatment is applied to the wiper, there is a risk of the increase in elution of a treatment agent when it is used for the wiping operation with an organic solvent.
Therefore, care must be taken in accordance with the conditions under which the wiper is used.
On the other hand, cellulosic fibers are excellent in water-absorption property, have less eluate, and are durable in use at a high temperature. However, they are not thermoplastic and, therefore, it is impossible to prevent the generation of dust and the release of fiber debris from the cut end face of the fabric.
Various methods have heretofore been proposed to decrease the amount of potential lint of wipers used in clean rooms required to have a high degree of cleanness. For example, in Japanese unexamined Patent Publication (Kokai) No. 2-45017 (Texwipe), a sheet composed of a thermoplastic fabric material is cut to have a given size, and a fused edge of thermoplastic fiber is provided at the periphery of the sheet, thereby preventing lint from being generated from the periphery of the cut faces or edges of the fabric. Since merely heat cutting the cut faces is not sufficient for suppressing the generation of lint, it is attempted that the generation of lint is reduced by fusion-bonding the thermoplastic fibers along the cut edge of the sheet over a given width. The sealed portion of the edge becomes film-like because the thermoplastic fibers are fused with heat and solidified again. Since the orientation and crystallization of the resin in this portion is insufficient, the tear strength and tensile strength thereof are deteriorated. Accordingly, it is necessary to increase the width of the fusion-bonded portion so that the fabric is not broken. For the above-mentioned reason, the wiper has a hard edge and is poor in flexibility and ease of handling. That is, since four corners are pointed, if the wiper is used for wiping a softer article, care must be taken not to damage the same. The above-mentioned problem regarding the edge is not solved even if a wiper is of a structure in which a material excellent in liquid absorption property is inserted into the interior of the sheet-like material.
The U.S. Pat. No. 5,069,735 (Milliken) proposes a method for cutting a wiping cloth of a predetermined size from a knitted fabric by using hot air or laser beam. According ito this method, it is possible to suppress the-release of lint by heat-fusing thermoplastic fibers situated at the edge along the periphery of the sheet. However, this method fails to prevent the edge from becoming film-like, and the problem of generation of lint and deterioration of physical properties such as a tear strength is still unsolved.
The U.S. Pat. No. 3,810,810 and British Patent No. 1,088,861 (Milliken) propose methods similar to that proposed by the above-mentioned Japanese Unexamined Patent Publication (Kokai) No. 2-45017 wherein a sheet is cut and the edge is sealed by using a hot roller or the like.
The U.S. Pat. No. 5,229,181 (Amber Technologies) discloses a wiper having a bag-like form prepared by heat-cutting a continuous tubular knitted fabric in the direction transverse to the longitudinal direction. The wiper of a bag-like structure has two edges of a continuous stitch structure and the other two edges which are cut while being thermocompression-bonded to melt the end portions of the cut fibers for the purpose of preventing lint from being released from the cut portion. Accordingly, there are problems common to those of the wipers proposed by the U.S. Pat. Nos. 5,069,785, 3,810,810, Japanese Unexamined Patent Publication No. 2-45017 or others. In this regard, a sheet-like wiper is also proposed which is prepared by partially fusion-bonding a knitted fabric in a bag-like form with an embossing roll. This wiper has a lower liquid-absorption property but is improved in dimensional stability and mechanical properties because of its single-sheet form.
All the wipers in the prior art described above can achieve the object of decreasing the generation of lint and detached fiber debris in a static state thereof. However, the wipers have been unsatisfactory for reducing the generation of dust and the release of fiber in the situation of practical use (when the wipers are subjected to stress such as stretching, creasing or scuffing or thereafter). Moreover, the wipers have not sufficiently had other required functions, for example, a water-absorption property, elution property in water and organic solvents, and ease of handling and safety thereof during the actual process and operation of the user. In addition, all the wiper must be prepared by cutting a knitted fabric accompanied with the cutting of loops of yarns forming the knitted fabric. As a result, the yarns have numerous cut points of fibers therein, and a special treatment is required for preventing lint and detached fiber debris of cut segments of fibers from being released from the cut faces. Since the fusion bonding is employed for preventing the release of fiber debris and sealing lint at the cut face of the knitted fabric, use of thermoplastic fiber or composite fiber containing the same is substantially necessary. This means that cellulosic fiber is substantially excluded from being used as-a material for a wiper, which is one of the optimum materials in view of the liquid-absorption property, resistance to solvent, and the small amount of elution component. When the sealed portion is made as small as possible in the fusion-bonding process for enhancing the ease of handling during the use, fine fiber segments are liable to be released, resulted in an unsatisfactory suppression of dust generation.
An object of the present invention is to provide a wiper composed of a fibrous fabric having a very low dust-generation property usable in a clean room.
Another object of the present invention is to provide a lint-free wiper usable in a clean room of a high degree of cleanness of at least Class 100.
A further object of the present invention is to provide a technology capable of providing a lint-free wiper composed of fiber material by a simple means, which wiper assuredly satisfies a performance optionally required at any stage of used.
According to the present invention, in a wiper composed of a fibrous fabric, cut ends of fibers present in a wiper, which are a cause of dust generation, are successfully reduced by forming the periphery of the fabric substantially with loops of yarns forming the fabric.
In other words, according to the present invention, a lint free wiper is provided, wherein the edge of a fabric is substantially composed of loops of yarns forming the fabric.
The wiper of the present invention is of a flat, cylindrical or bag-like shaped structure wherein all surfaces extending from a wiping surface in a central region of a flat surface to the periphery thereof are formed of a fabric.
The fabric includes a woven fabric and a knitted fabric. In this connection, to achieve the object of the present invention, the woven fabric includes those obtained from a loom capable of continuously inserting a weft yarn, such as a fly loom or a shuttle loom, and the knitted fabric includes a warp knit fabric, a weft knit fabric, a circular knit fabric or others.
Upon the production of the lint-free wiper of the present invention-having the structure described above, the knit fabric can be formed as a fabric structure having the periphery substantially formed of loops of knitted yarn alone. That is, the wiper is obtainable while completely excluding the formation of cut faces due to the use of a blade or the like. Thereby, the knit fabric is particularly suitable for the present invention from the technical and commercial view points, as will be apparent from the aspects and examples of the present invention described later.